1. Field of Invention
This invention relates generally to a water distribution system, and in particular to a water distribution system having a dual use water treatment unit.
2. Background of the Invention
Water treatment units (WTUs) for the purification of potable water on aircraft or other vehicles have been known for years. For example, International Water-Guard Industries Inc. provides different models of flight-certified water treatment units for aircraft applications. Certain known WTUs employ ultraviolet (UV) lamps that inactivate micro-organisms including pathogens by irradiation with UV light in the germicidal wavelength range. This process is customarily referred to as UV disinfection. The WTUs sometimes are also supplied with either sediment or activated carbon filters for the removal of fine particulate matter or dissolved chlorine or organic matter to improve the taste of the water.
In known aircraft water treatment systems, WTUs are generally installed in one of two locations on an aircraft. They may be installed at the exit of a potable water storage tank so that all the water delivered from the tank to aircraft points of use is disinfected, whether the water is delivered under pressure to points of use on demand or water is circulating continuously. Alternatively, WTUs may be installed at selected points of use on the aircraft, such as galleys where food and beverages are prepared or for VIP showers.
Aircraft manufacturers or aircraft completion centers have enquired about treating water as it is being uploaded onto the aircraft on the ground. Proposed solutions have included integrating additional WTUs into the aircraft potable water fill system. These proposals are not optimal due to the additional cost of WTUs that would be used during the fill operation, and the weight and complexity of the WTUs should they be installed on the aircraft. Another drawback is that past proposals for WTUs to be used for fill operations are installed further from the point of water use and thus are generally regarded as providing less protection to human health since there is more opportunity for contamination downstream of the treatment units.
Disadvantages of conventional systems are known, and exemplified by prior art. For example, U.S. Pat. No. 5,660,721 discloses a conduit 22 that connects a diverter valve 23 to the WTU 26, and conduit 48 connects the WTU 26 to diverter valve 50, such that when valve 23 is in the fill position water flows from the fill port 16 to the WTU 26 through conduit 22 and when diverter valve 50 is in the supply position water flows from the WTU 26 to the point of water use device 12 through conduit 48. Therefore different conduits are used to transport the water to and from the WTU.
U.S. Pat. No. 5,045,215 discloses a system for removing contaminants from domestic water supplies using an accumulator tank 68; however, the purified water from this tank is always pumped to a point of use device (see FIG. 2 and column 12 lines 16 to 54); there is no disclosure or suggestion that the water flow can be diverted by a diverter valve for any purpose, let alone to allow a water treatment unit to treat water during a fill operation.
U.S. Pat. No. 7,775,374 discloses a water purification unit comprising a pump 114 to draw water from a water source 102; this water is passed through a main filter 132 to purify the water and dispensed through an outlet 136 (Abstract, FIG. 1). The pump always pumps water from the water source to the outlet; notably, this reference does not disclose or suggest that the water can be diverted by a diverter valve for any purpose, let alone to allow a filter (or other water treatment unit) to treat water during a fill operation, e.g. to fill the expansion tank 150.
Instead, it discloses an optional prefilter 120 that can be provided between the pump and an expansion tank 150 to remove larger particulate, bacteria, viruses. As noted above, prior art water treatment systems are known to use multiple water treatment units to treat water during a fill operation, as well as to treat water during a supply operation; however, such approaches are not optimal due to the additional cost, weight and complexity of using multiple water treatment units. U.S. Pat. No. 7,775,374 is no different. Using multiple filters presents the same challenges that the present invention is intended to overcome.